1. Technical Field of the Invention
This invention relates to reduction and contained decomposition of organic waste material, and more particularly, to a unitized process and apparatus for reducing and in-vessel composting raw food waste and biodegradable eating utensils and trays, yard waste, and newspapers, in combination with associated organic packing materials such as cardboard and paperboard containers, into two useful compost components, one liquid and one relatively dry.
2. Background of the Invention
According to published sources, in all, the United States generates approximately 208 million tons of municipal solid waste per year. Public and private sectors, alike, are facing increasing cost and difficulty in disposing of their enormous and increasing tonnage of solid waste and garbage in an environmentally sound and economically acceptable manner. Historically, refuse or garbage has been collected and disposed of by one of several inexpensive means, such as open burning, dumping in waterways, or dumping in common landfills.
As the ecological impact of such practices became evident, the demand for safer practices grew. Three methods emerged as environmentally suitable means for safe refuse disposal: (1) sophisticated landfills with costly structures and controls designed to prevent leaching into surrounding ground water; (2) controlled incineration; and (3) composting in which the compost product has a reduced toxicity suitable for subsequent disposal in a landfill. However, according to data from the United States Environmental Protection Agency, the number of operating landfills in the U.S. has dropped by more than half in the past ten years.
Although municipal incinerators are more environmentally friendly than they were a generation ago, they continue to release gases and solid particles that may harm human health, damage property, and kill plants. The biggest components of all municipal solid waste are compostable; yard waste, corrugated boxes, and food waste.
The benefits of composting have long been known. Though not a fertilizer, it is a useful soil conditioner that improves texture, air circulation, and drainage. Compost moderates soil temperature, enhances nutrient and water-holding capacity, decreases erosion, inhibits weed growth, and suppresses some plant pathogens. High quality compost is being used for and marketed as a soil amendment and as mulch for landscaping, farming, horticulture, and home gardens. Compost can also be used as landfill cover or in land reclamation projects.
There is a large body of art relating to in-vessel composting, some providing useful descriptions of the basic biological process. Existing in-vessel composters typically have one or more of the following general short-comings. (1) the system is too complex and the cost to purchase and operate is cost prohibitive to small businesses and organizations, (2) the system requires an extended processing time of generally greater than three weeks, such that the necessary capacity of the system becomes cumbersome and/or restrictive, or (3) the process produces output material which is less than 60% composted when removed from the vessel, requiring additional composting and processing time prior to curing.
There remains a need for an affordable, simple to operate, energy efficient, in-vessel composting system that substantially reduces the volume and weight of the input materials, and processes a useful end product of commercial value.
Disease-suppressive compost is not made by accident. It comes about by carefully monitoring the atmosphere inside of a composting vessel to ensure that the temperature, moisture, and oxygen levels are all maintained at proper levels throughout the entire process. Varying species of bacteria present in the composting vessel will break down and organic materials into the output compost mixture. And, as temperatures rise and fall in the compost, different bacterial species will become more or less active. Psychrophilic bacteria, mosophilic bacteria and thermophilic bacteria each operate best within specific temperature ranges. Furthermore, with sufficient oxygen, microorganisms produce energy, grow quickly, consume more material and make nutrients available for plant growth. Without oxygen, aerobic bacteria die off and anaerobic bacteria take over. They will break down the material, but more slowly, and with an accompanying unpleasant odor. Offensive odors are produced only when the material in the system is allowed to become anaerobic, not a normal condition in the practice of this invention.
To provide a simple, reliable, efficient, in-vessel composting system, it is most useful to optimize the apparatus to a selected, well-defined waste stream, thus reducing the processing variables and simplifying the apparatus and operation. This technique offers the user a composting process and apparatus that produces a more consistent, higher quality, nutrient rich, end product.
The invention, in it""s simplest form, is an integrated or unitized reduction and composting process and system for the recycling of food waste and associated organic waste materials such as cardboard and paper board packaging materials, into a nutrient-rich liquid compost xe2x80x9cteaxe2x80x9d and bulk organic end product that are manageable, useful, and inoffensive. This waste stream provides an abundance of nitrogen and moisture, both important in the process. The amount of carbon and moisture absorbing bulk input can be varied, based on process conditions, by adding supplemental organic materials such as cardboard and paper board. The invention will accept traditional bulking agents such as sawdust and wood chips if desired, but is specifically designed to shred corrugated cardboard, found in many waste streams such as that of restaurants and supermarkets, to optimum size for the composting process of the invention.
The system is tolerant of a limited amount of incompatible solid contaminants that may be present in particular applications or installations. The invention utilizes a continuous four-step process which has approximately a three week throughput cycle, consisting of shredding to the optimal particle size, then mixing and composting the bulk materials through a three step, in-vessel process, while draining the excess liquid at the first stage and reprocessing it into compost tea through the finished bulk product. The apparatus is self-contained to provide for continuous input of raw waste, generating a bulk output of nutrient-rich, organic liquid and bulk compost materials of significantly less total volume and weight than the input materials.
Particle size is an important aspect of the composting process. If the waste particles are too large, the relatively small ratio of surface area to mass inhibits the start of the process. Shredding the material at the point of input offers a large advantage in this respect. On the other hand, if the input material is shred too small, porosity and the ability of the material to be aerated is greatly diminished. As a result, bacteria is less able to act. For the waste stream to which this invention is directed, an optimal particle size has been determined to be about 3 cubic inches. A shredder in the infeed stage provides for this requirement.
After the shredder sizes the input material, the material is directed into the first chamber of a three-chambered rotating drum. While three different drums would offer some flexibility in the control of the process, one drum and drum drive provides efficiency in the design that is reflected in cost and simplicity. A drainage mechanism in the first chamber diverts excess liquid into a batched, bypass system for later processing through the finished bulk compost product into compost tea. The drum and liquid handling systems are encased in an insulated enclosure, assuring that there will always be a surplus of heat. The apparatus is arranged on a base frame with the drum oriented horizontal, again contributing to simplicity.
Periodic and temperature-based drum rotation, in conjunction with the periodic operation of an exhaust fan for air exchange, provides necessary cooling control within the drum. Oxygen, present in the specified waste stream materials and moisture content, and in the makeup air supplied by the exhaust fan ,is present at adequate levels to sustain the composting process. Aeration for drying, cooling, and supplying oxygen, is accomplished by the incremental rotations of the drum throughout the process.
Chamber to chamber progression is intentionally restricted to gradual, full diameter tumbling of the materials in each chamber, with a continual incremental spill over through a slightly larger diameter annular, axial port into the next chamber. The continuous spill over into the next chamber permits the remaining material to maintain a small but consistent forward progression through the drum as it tumbles, without inconsistent acceleration of portions of the material by intentionally angled blades, buckets or augers. This assures that the process progresses at a consistent rate in each chamber, and that the end product will be a homogenous, fully composted end product. A substantial residual volume of material is retained in all chambers at all times, further forward movement through the system and discharge of end product being dependent on regular, continuing input at the infeeding end.
Once inside the first chamber, the material will reside there for approximately 2 to 5 days as it is slowly churned into a homogeneous mixture, the excess liquid draining out through ports into a collection system, with each new batch of input material being quickly engulfed in the on-going composting process. A small mixing vane or like feature promotes tumbling, but does not contribute directly to forward movement through the system. Heat is readily generated by the active thermophilic bacteria, supplied with nitrogen and carbon, both inherently present in the mixture. The material is advanced to the next chamber as described above.
The center or second chamber is the main composting furnace. Having been pre-conditioned in the first chamber, the new material is quickly fully absorbed in the process. The temperature within this second chamber is maintained within the range of 100 to 150 degrees Fahrenheit, preferably higher than 131 degrees Fahrenheit to ensure pathogen destruction if the waste food mix includes meats and dairy products. It is also necessary to maintain this temperature range to kill any seeds present within the waste stream. In contrast, from practice it was found that waste stream materials other than those containing pathogens, such as fruits, vegetables, paper, etc. will degrade to compost at temperatures as low as 95 degrees Fahrenheit due to the activity of mesophilic bacteria.
However, it should be noted that while there are no pathogenic materials to contend with, seeds within the waste stream will not be killed at such a low temperature. Just as important, the temperature of the mixture material should not exceed 158 degrees Fahrenheit as the beneficial anaerobic bacteria will begin to die off as temperatures rise above this level.
The volume of the second chamber is such that during continuous use and operation of the system, the bulk of the mixture is retained for approximately 4 to 10 days while the composting action reduces the volume of the output mixture by typically as much as 85 to 90 percent. As a result of this decrease in volume, the density of the material is increased.
A mixing vane or similar limited internal structure, as in the first chamber, promotes tumbling only. A small amount of mixture is being regularly passed into the third chamber, again by the incremental rotation and gradual flow through the next larger port. A substantial amount of residual material remains working in the second section at all times.
By the time the material reaches the third chamber, its volume has been greatly reduced due to the composting process. Due to the reduction of the material within the first two chambers, material flows into the third chamber at a much slower rate. The material, therefore, is not as quickly displaced from the third chamber. As a result, material resides in the third chamber for a longer duration, allowing the material to finalize the composting process and begin to cure. This chamber is equipped with a greater number of vanes or equivalent structures to increase tumbling and to reduce and break up any clumps in the compost material received from the second chamber.
In practice, even with less than ideal peak temperatures through the first and second chambers, seedling vegetation growth has been witnessed in the third chamber material. This is noteworthy because vegetation is unable to grow in active, unfinished compost material. This demonstrates that resultant material in the third chamber has completed the composting process and is partially cured prior to exiting through the third chamber""s output port.
Meanwhile, the excess liquid is batched and held at the same elevated temperature as the middle chamber, for three days or more, or in accordance with regulatory requirements, then percolated through the third chamber to be enriched by the highly concentrated nutrients present there, and continuously drained from there into a final collection system for batch removal on a periodic basis.
Expanding now on the compost tea aspects of the above disclosure, it as been determined that excessive liquid in the food waste materials hinders the biological activity of the composting process in the drum. Additionally, there is a significant commercial interest in the xe2x80x9cteaxe2x80x9d, a liquid product issuing from composting processes, if it can be produced with a consistently high degree of purity and quality.
To these ends, one purpose of the invention is to provide a dual track, liquid and bulk waste composting process that removes excess liquid from the food waste entering the drum so the second chamber in particular does not have excess liquid which will hinder the biological activity of the dry track bulk matter composting process. Another goal is to process the liquid into a useful end product, so called xe2x80x9ccompost teaxe2x80x9d, in a parallel path, liquid track, within the same overall apparatus, and to coordinate the processing of the tea for collection on the same schedule as the relatively drier, bulk matter compost product.
The invention described above includes means for extracting excess liquid from the first chamber of the drum, maintaining the liquid at elevated temperature for at least 72 hours, and then percolating it through the final stage compost product in the third chamber of the drum and draining it into a separate holding tank below the drum. The xe2x80x9cteaxe2x80x9d product is then available for removal and reuse as a liquid supplement to various organic and gardening processes.
As a result of the lower moisture content of the food waste during its processing in the drum, the final compost product is greatly reduced in volume, and is of generally better and more consistent quality and more easily handled than otherwise.
It is an object of the invention to provide an apparatus for the efficient, in-vessel composting of foot waste and associated organic waste such as cardboard and paperboard packaging materials.
It is another object of the invention to create, essentially from food waste, two useful compost products, one being a liquid xe2x80x9cteaxe2x80x9d product and the other being a relatively drier, bulk matter compost product.
Still other objects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein I have shown and described only a preferred embodiment of the invention, simply by way of illustration of the best mode contemplated by me on carrying out my invention.